Welcome! I have a Mini Cooper S Works and an Alfa 147 JTD so can give you a pretty good comparison! The Mini Handles a lot better, and feels like its built better but for a long journey/touring the Alfa surprisingly wins every time on comfort and practicality. My previous Cooper S was a 163BHP version and the JTD engine in the Alfa could keep up just fine despite being only 115BHP (it did have more torque though)!
The Alfa has been more reliable but is more expensive when work does need doing, if you can afford it get both, if you want a fun car for back road blasts and track days get the MINI, if you do long journeys keep the Alfa! Don't wanna put you off the MINI though, out of the two its my favourite!